Electrical connections with deformable contacts

ABSTRACT

An interposer for interconnection between microelectronic circuit panels has contacts at its surfaces. Each contact has a central axis normal to the surface and a peripheral portion adapted to expand radially outwardly from the central axis responsive to a force applied by a pad on the engaged circuit panel. Thus, when the circuit panels are compressed with the interposers, the contacts expand radially and wipe across the pads. The wiping action facilitates bonding of the contacts to the pads, as by conductive bonding material carried on the contacts themselves.

This is a division of application Ser. No. 08/277,336 filed Jul. 19,1994 now U.S. Pat. No. 5,590,460.

FIELD OF THE INVENTION

The present invention relates to the field of electrical circuitry, andmore particularly relates to layered circuit structures such asmulti-layer circuit boards, to components and methods utilized infabrication of such structures and to methods of making the same.

BACKGROUND OF THE INVENTION

Electrical components are commonly mounted on circuit panel structuressuch as printed circuit boards. Circuit panels ordinarily include agenerally flat sheet of dielectric material with electrical conductorsdisposed on a major, flat surface of the sheet or on both majorsurfaces. The conductors are commonly formed from metallic materialssuch as copper and serve to interconnect the electrical componentsmounted to the board. Where the conductors are disposed on both majorsurfaces of the panel, the panel may have via conductors extendingthrough the dielectric layer so as to interconnect the conductors onopposite surfaces. Multi-layer circuit panel assemblies have been madeheretofore which incorporate plural, stacked circuit panels withadditional layers of dielectric materials separating the conductors onmutually facing surfaces of adjacent panels in the stack. Thesemulti-layer assemblies ordinarily incorporate interconnections extendingbetween the conductors on the various circuit panels in the stack asnecessary to provide the required electrical interconnections.

Electrical components which can be mounted to circuit panel structuresinclude so-called “discrete” components and integrated circuits whichinclude numerous transistors on a single chip. Chips of this nature canbe mounted to commonly referred to as “chip carriers” which arespecialized circuit panel structures. A chip carrier may be incorporatedin a package which is mounted to a larger circuit board andinterconnected with the remaining elements of the circuit.Alternatively, the chip can be mounted directly to the same circuitpanel which carries other components of the system. This arrangement isordinarily referred to as a “hybrid circuit”. Relatively large circuitpanels are commonly made of polymeric materials, typically withreinforcement such as glass, whereas very small circuit panels such asthose used as semiconductor chip carriers may be formed from ceramics,silicon or the like.

There have been increasing needs for circuit panel structures whichprovide high density, complex interconnections. These needs areaddressed by multilayer circuit panel structures. The methods generallyused to fabricate multi-layer panel structures have certain seriousdrawbacks. Multi-layer panels are commonly made by providing individual,dual sided circuit panels with appropriate conductors thereon. Thepanels are then laminated one atop the other with one or more layers ofuncured or partially cured dielectric material, commonly referred to as“prepregs” disposed between each pair of adjacent panels. Such a stackordinarily is cured under heat and pressure to form a unitary mass.After curing, holes are drilled through the stack at locations whereelectrical connections between different boards are desired. Theresulting holes are then coated or filled with electrically conductivematerials, typically by plating the interiors of the holes to form whatis called a plated through hole. It is difficult to drill holes with ahigh ratio of depth to diameter. Thus, the holes used in assembliesfabricated according to these prior methods must be relatively large andhence consume substantial amounts of space in the assembly. These holesordinarily extend from the top or bottom of the stack. Even whereinterconnections are not required in the top or bottom layers, spacemust be provided for holes to the pads for more effective contact. Thetabs are maintained in engagement with the pads by the resilience of theelastomeric sheet and the posts; there is no permanent bond formed.

Patraw, U.S. Pat. Nos. 4,716,049; 4,902,606; and 4,924,353 describemicroelectronic connection schemes using deformable contacts protrudingupwardly from a substrate. Each contact has a dome-like tip and aplurality of legs extending downwardly from the tip to the substrate.These contacts are formed by selective deposition of aluminum on apedestals of a fugitive material such as potassium chloride or aphotoresist using a shaped mask. The pedestals are removed afterdeposition.

Dery et al., U.S. Pat. No. 4,729,809 discloses the use of ananisotropically conductive adhesive material disposed between opposingsublaminates, the adhesive composition having sufficient conductivityacross the relatively small spaces between conductors on adjacent layersto form an electrical interconnection therebetween, but having lowconductivity across the relatively large spaces between adjacentconductors on the same surface so that it does not produce an unwantedlateral interconnection along one surface.

Berger et al., U.S. Pat. No. 4,788,766 uses conductor bearing circuitlamina having hollow, eyelet-like via structures, each such viastructure having a rim protruding vertically from the surroundingstructure. Each such via structure is provided with a thin layer of aconductive bonding material. In making the multi-layer structure,dielectric bonding films are interposed between the circuit bearinglamina. The dielectric films have apertures in locations correspondingto the locations of the eyelet structures, in the adjacent circuitbearing lamina. Thus, the upstanding rims of the eyelet structures canbear upon one another when the assembly is forced together under heatand pressure. The layers of conductive bonding elements and soldercooperatively form an interconnection between the adjacent circuitboards.

Evans et al, U.S. Pat. No. 4,655,519 describes a connector with numerousstrip-like contact springs disposed in holes in a flat dielectric body,together with other spring elements. The ends of the strips protrudefrom opposite surfaces of the body. These are adapted to compress whenelectronic elements are engaged with the body surfaces, so that the endsof the strips engage pads on the electronic elements. Walkup, U.S. Pat.No. 5,167,512 discloses a further system using springs disposed in holesin a dielectric body.

Grabbe, U.S. Pat. No. 5,228,861 describes a connector having asheet-like dielectric body with numerous generally X-shaped springcontact elements, each having four arms, lying on a first side of thesheet. Two arms of each X-shaped element are bent inwardly toward thesheet, and extend through holes in the sheet so that the tips of thesearms protrude above the second, opposite face of the sheet. The othertwo arms are bent away from the sheet, and hence protrude from the firstsurface. When the connector is placed between circuit panels, eachX-shaped element is compressed between mating pads of the circuitpanels, causing the bent arms to flatten and causing the tips of thearms to wipe the surfaces of the pads. After engagement, the contact ismaintained by the resilience of the arms.

Bernarr et al, U.S. Pat. No. 4,548,451 describes a connector orinterposer having a sheet-like elastomeric body with crushableprotrusions extending outwardly from oppositely-directed surfaces. Tabsformed from a metal-coated flexible film extend on both surfaces of thebody, and overlie the protrusions. The tabs on opposite sides areconnected to one another by vias. When the interposer is engaged betweencircuit panels, the tabs and posts are crushed between contact pads onopposing panels, and the tabs assertedly wipe pass through these layersso as to provide needed interconnections in the middle layers.Accordingly, substantial amounts of the available surface area on thepanels must be allocated to the holes and to accommodate tolerance zonesaround the holes. Moreover, the electrical interconnections formed bydepositing conductive materials in such drilled holes tend to be weak.The drilling method and the general nature of the laminates used thereinis described, for example in Doherty, Jr., U.S. Pat. No. 3,793,469; andGuarracini, U.S. Pat. No. 3,316,618.

Various alternative approaches have been proposed. Parks et al., U.S.Pat. No. 3,541,222; Crepeau, U.S. Pat. No. 4,249,032; Luttmer, U.S. Pat.No. 3,795,037; Davies et al., U.S. Pat. No. 3,862,790, Fox U.S. Pat. No.4,954,878, and Zifcak, U.S. Pat. No. 4,793,814 all relate generally tostructures which have metallic or other conductive elements arranged atrelatively closely spaced locations on a dielectric sheet with theconductive elements protruding through the dielectric sheet in bothdirections. Such a sheet may be sandwiched between a pair of circuitboards and the circuit boards may be clamped or otherwise held togetherso as to provide mechanical engagement between conductive elements onthe adjacent faces of the circuit boards and the conductive elements ofthe composite sheet. In each of these arrangements, the conductiveelements, the composite sheet or both is resilient or malleable so as toprovide for close engagement between the conductive elements of thecomposite sheet and the conductors on the circuit boards.

Beck, U.S. Pat. No. 3,616,532 and Dube et al., U.S. Pat. No. 3,509,270describe variants of this approach in which resilient elements are usedwith a fusible solder. These elements are mounted on insulating boardswhich are then stacked between printed circuit layers. The assembly isheated so as to melt the solder, thereby freeing the resilient elementsso that the resilient material on the rims of the abutting eyelets aresaid to form bonds between the abutting eyelet structures.

Other structures for forming multilayer electronic assemblies are taughtin Dux et al., U.S. Pat. No. 5,224,265 and Ehrenberg et al. U.S. Pat.No. 5,232,548, which use sublaminates made by depositing a dielectricmaterial onto a perforated metal sheet, as by vapor-phase polymerizationor electrophoretic bonding, to form a dielectric sheet with vias. Thevias are filled with a flowable joining material such as a metal-loadedpolymer. These structures are stacked and heated to join the vias intounitary vertical conductors.

Other multilayer assembly systems using flowable conductive materials tojoin structures in stacked elements are disclosed in Bindra et al., U.S.Pat. No. 5,129,142. Still further improvements are disclosed U.S. Pat.No. 5,282,312 of Thomas H. DiStefano et al. The '312 patent discloses asbackground certain lamination techniques or methods of makingmulti-layer circuit assemblies using flowable conducting materials.

Despite these and other efforts in the art, there are needs for stillfurther improvement.

SUMMARY OF THE INVENTION

The present invention addresses these needs.

One aspect of the present invention provides an interposer for makingconnections to electrical contacts on the surface of a microelectronicelements such as a circuit panel, a semiconductor chip or other elementhaving a contact-bearing surface. The interposer includes a body havinga first major surface, such that the body defines horizontal directionsparallel to the first major surface and vertical directionsperpendicular to the first major surface. The interposer further has aplurality of conductors in the body, such as via conductors extending inor through the body. The interposer further includes contacts at thefirst major surface of the body electrically connected to theconductors. Each contact extends over the first surface of the bodygenerally radially outwardly from a central axis which is perpendicularto the first surface. Thus, each contact extends in a plurality ofhorizontal directions away from the axis and away from the junction ofthe contact with the conductor. Each contact has a periphery remote fromthe central axis. The contacts are adapted to deform so that theperiphery of each contact will expand generally radially outwardly, awayfrom the axis, in response to a force applied to the contact directedtoward the body. In use, the contacts are engaged with correspondingconnection pads of a circuit panel or other microelectronic element whenthe element is juxtaposed with the first surface of the interposer. Thepanel or other element can then be forced toward the body, so that thepads apply vertical forces to the contacts. As each contact expandsoutwardly in response to the vertical force, it wipes across the surfaceof the mating pad. The wiping action removes oxides and othercontaminants from the mating surfaces to provide an effective,low-resistance electrical connection between the pads and the contactsand, in preferred embodiments, to facilitate bonding of the contacts andpads.

The contacts desirably are arranged to deform so that the periphery ofeach contact moves vertically downwardly toward the body as theperiphery moves radially outwardly. In the initial, undeformedcondition, the periphery of each contact may be spaced vertically abovethe surface of the body. Each contact may include a central portionadjacent the axis which may be in engagement the body, whereas aperipheral portion of the contact may extend radially outwardly from thecentral portion and vertically upwardly, away from the body. The centralportion of each contact may be connected to a conductor, so that thecontact extends radially outwardly, atop the surface of the body, fromthe conductor. Each contact may be generally in the form of a body of arevolution about the vertical central axis. Thus, the peripheral portionmay be a shell in the form of an upwardly and outwardly flaring ofrevolution about the central axis. In this instance, the expandingaction of the contact is reminiscent of the setting of a rivet.

Alternatively, the periphery of each contact may be non-circular. Thus,each contact may include a plurality of tabs extending generallyradially away from the central axis, each such tab having a tip remotefrom the axis and remote from the conductor. Desirably, the tabs of eachcontact are disposed in a substantially symmetrical pattern about thecentral axis and about the junction with the conductor, so that the tabsextend generally symmetrically in radial directions away from thecentral axis, and away from the conductor. A preferred symmetricalpattern includes four tabs disposed at equally spaced intervals aroundthe central axis, such that the tabs define a quatrefoil pattern.

When the tips of the tabs are engaged by a pad on a circuit panel orother microelectronic element and forced downwardly towards the body,the tip of each tab will bend downwardly and outwardly, away from thecentral axis. Thus, the tabs of the contact unfold away from oneanother, to provide an effective wiping action against the surface ofthe engaged pad. Although the present invention is not limited by anytheory of operation, it is believed that this outward movement of thetab tips is produced at least in part by the bending of each tabgenerally around the radially inward or proximal end of the tab andaround the adjacent regions of the body itself. The body surface mayhave depressions housing the central portions of the contacts, and mayalso have outwardly-flaring walls surrounding the depressions. Each tabmay be arcuate, and may conform to the outwardly-flaring wall.

Preferably, the contacts include bonding materials adapted to facilitatethe bonding of the contacts to a mating pad engaged therewith. Thebonding material may be selected from a group consisting of solders,brazing alloys, diffusion bonding alloys, eutectic bonding alloys andconductive materials incorporating polymers. The contacts may bemetallic and may be formed integrally with the associated conductors.The interposer body preferably is a lamellar structure, such as asheet-like or platelike structure, and defines a second major surfacefacing in the opposite direction from the first major surface. At leastsome of the conductors may be through conductors having second endsdisposed adjacent the second major surface. In this case, the interposerhas second end contacts attached to the second ends of the conductors.Each such second end contact may be configured in the same manner as thefirst end contacts discussed above. Thus, each second end contact mayextend radially outwardly away from a central axis which isperpendicular to the second surface, and may extend from a second end ofa conductor connected at its first end to one of the contacts on thefirst surface. The contact desirably is adapted to deform so that theperiphery will expand radically outwardly, away from the axis and fromthe conductor second end in response to a vertical force on the secondend contact. Such interposers can be used, for example, between pairs ofcircuit panels or other microelectronic elements.

The contacts and the conductors may constitute portions of continuous,generally tubular vias extending through a hole in the body and flaringoutwardly at both ends of the hole. The interposer body may have a heatactivatable adhesive, a thermoplastic or other flowable dielectricmaterial at the surfaces of the body, so that the interposer can form asubstantially void free dielectric seal with the body of a circuit panelor other microelectronic element engaged therewith. Where the conductivebonding material on the contacts is activated by heat, the adhesive orthe flowable dielectric material on the body may be arranged foractivation at approximately the same temperature as the flowableconductive material.

A further aspect of the invention provides a microelectronic connectioninterposer having a body with a first horizontally extensive surfacehaving a principal plane and a plurality of contacts disposed in anarray on the body at said surface. Each contact includes a centralportion and a peripheral portion extending outwardly from the centralportion. The central portion may be recessed vertically from theprincipal plane of the surface, whereas the peripheral portion mayextend at or vertically above the principal plane. Desirably, theperipheral portion of each contact is non-circular and may include tabsas aforementioned projecting away from the central portion. The body mayinclude a plurality of indentation in the first surface, each suchindentation having a central axis generally perpendicular to the firstsurface and having walls flaring generally radially outwardly up awayfrom the central axis so that the indentation widens progressively fromthe base of the indentation to the opening of the recess at theprincipal plane.

Another aspect of the present invention provides methods of making amulti-layer circuit. A method according to this aspect of the presentinvention desirably includes the step of stacking a microelectronicelement such as a circuit panel and an interposer so the first surfaceof the interposer confronts a surface of the microelectronic element.The interposer may be an interposer as described above, having a body,having conductors and having contacts joined to the conductors, eachcontact extending over the surface of the body and extending radiallyoutwardly from its juncture with the conductor to a peripheral portion.The method includes the further step of compressing the stackedmicroelectronic element and interposer so as to forcibly engage theperipheral portions of the contacts with the pads of the microelectronicelement, thereby expanding the peripheral portion of each contactradially outwardly, away from the central axis and away from theassociated conductor. Thus, the peripheral portion of each contact moveshorizontally with respect to the engaged pad and wipes the surface ofthe pad. Preferably, during the compressing step, each peripheralportion also moves vertically downwardly, i.e., toward or into the bodyof the interposer.

The stacking step may include the step of stacking a plurality ofcircuit panels and one or more interposers in interleaved, verticallyalternating arrangements so that one interposer is disposed between eachpair of circuit panels and so that oppositely directed first and secondsurfaces of each interposer confront the mating surfaces of the panels.In this arrangement, the conductors of each interposer desirably includethrough or via conductors extending through the body and having contactsat both ends of each conductor, on opposite surfaces of the interposer.The contacts on the opposite surfaces engage pads on the two neighboringcircuit panels on opposite sides of the interposer. Thus, when thecontacts are engaged with the pads of the circuit panels, the throughconductors will interconnect the pads on the neighboring circuit panelwith one another. In preferred processes according to this aspect of thepresent invention, the wiping action of the contacts provides forreliable electrical bonding between the circuit panels. Moreover, thevertical movement of the contact peripheral portions compensates fornonplanarity of the circuit panels and interposers. Preferred methodsaccording to this aspect of the present invention can provide reliableinterconnections and reliable multi-layer structures even with verysmall feature sizes. Thus, the spacings between adjacent pads on thecircuit panels and between adjacent contacts on each surface of eachinterposer may be about 1.0 mm or less.

Preferably, the method includes the step of bonding the contacts of theinterposers to the pads on the panels, by momentarily heating thestacked elements to activate an electrically conductive bonding materialat interfaces between the contacts and contacts. Preferably, the methodalso includes a step of activating a flowable dielectric material suchas an adhesive to flow at the interfaces between each of the interposerbodies and the adjoining microelectronic elements or panels so as tojoin the stacked elements into a substantially unitary mass. The flow ofthe dielectric material may occur concomitantly with the flow of theelectrically conductive bonding material. Where the peripheral portionsof the contacts overlie portions of the dielectric material of theinterposer body, softening of the dielectric bonding material tends tofacilitate vertical movement of the peripheral portions of the contacts.As the dielectric material softens, the peripheral portion of eachcontact may be displaced downwardly into the underlying dielectricmaterial.

Further aspects of the present invention includes methods of making acircuit assembly including the steps of stacking microelectronicelements such as a circuit panel and an interposer in a verticallysuperposed arrangement so that a first horizontally extensive surface ofthe interposer confronts a horizontally extensive surface of the circuitpanel and so that a plurality of electrically conductive contacts at thefirst surface of the interposer confront pads on the surface of thecircuit panel. The method further includes the step of compressing thestacked microelectronic elements and the interposer vertically so as toforcibly engage the contacts with the pads and cause the contacts todeform so that at least a portion of each contact engaged with the padmoves horizontally with respect to the engaged contact and wipes thesurface of the contact during the compressing step, and subsequentlybonding each contact to the engaged pad, as by activating a bondingmaterial at interfaces between the contacts and the pads by momentarilyheating the stacked elements. The bonding step may include diffusionbonding, soldering, brazing, eutectic bonding, activation of a polymericconductive adhesive or the like. The wiping action cleans the surfacesto facilitate effective bonding.

Still further aspects of the present invention provide methods of makingmicroelectronic interposers. Methods according to this aspect of thepresent invention preferably include the steps of providing a bodydefining a first surface and providing a first temporary layer on thefirst surface so that the temporary layer has apertures therein. Anelectrically conductive structural material such as copper or anothermetal is deposited in each aperture so that a layer of the structuralmaterial extends within the aperture and extends over at least a portionof the temporary layer, thereby forming contacts. The method alsoincludes the step of removing the temporary layer, leaving an outwardlyextending peripheral portion of each contact spaced away from thesurface of the body where the structural material was deposited on thetemporary layer. Desirably, the body has holes extending inwardly fromthe first surface in registration with the apertures in the temporarylayer and the structural material is deposited in the holes so that theconductors are formed integrally with the contacts.

Where the body has oppositely directed first and second surfaces, theholes in the body may extend from the first surface to the secondsurface and the method may include the step of providing a secondtemporary layer on the second surface with apertures in registrationwith the holes. Thus, the step of depositing the structural material mayinclude the step of depositing the structural material in the aperturesof the second temporary layer as well, so that the structural materialextends over part of the second temporary layer. The method may furtherinclude a step of removing the second temporary layer thereby leavingcontacts on the second surface integral with the conductors and with thecontacts on the first surface. The holes and the apertures in thetemporary layers may be formed so that walls of the holes of the bodyare substantially continuous with the walls of the apertures in thetemporary layers. Thus, the step of forming the holes in the body may beperformed after the step of applying the temporary layers with theirrespective apertures, as by removing material from the body using one orboth of the temporary layers as masks.

Desirably, each aperture in each of the temporary layers has a centralaxis and the temporary layer defines a wall at each aperture flaringoutwardly, away from the central axis of the aperture in the verticallyupward and outward direction and away from the associated surface of thebody. The step of depositing the structural material may include thestep of depositing a thin layer of metal on these outwardly flaringwalls. Thus, when the temporary layers are removed, the portions of thestructural material overlying the outwardly flaring walls will be spacedfrom the surface of the body and will slope progressively upwardly awayfrom the body in the radially outward direction from the central axis.

The step of providing the temporary layer may include the step ofdepositing the temporary layer material as an imperforate layer on thesurface of the body and then forming the apertures by masking theimperforate layer so that the mask has openings. The masked layer maythen be exposed to an isotropic etchant through the openings. Suchtreatment tends to form a generally cup-shaped surface. The structuralmaterial desirably is a metal such as copper, gold, nickel and the likewhich may be plated over the temporary layer. The temporary layer may beformed from a metal such as aluminum, tin or nickel, and the temporarylayer may be removed by a process such as caustic etching, leaving thestructural material intact. Alternatively, the temporary layer mayinclude a layer of a polymeric material such as a resist, or othermaterials which can be removed without damaging the structural material.

Other aspects of the present invention provide methods of makingmicroelectronic interposers using a body having a first surface, thefirst surface including a principal planar portion and a plurality ofopen indentations with vertical axes normal to the principal plane andwith walls flaring outwardly away from the axes. Methods according tothis aspect of the invention desirably include the step of depositing anelectrically conductive structural material in the indentations to forma layer on the outwardly-flaring walls, and controlling the extent ofthe layers in horizontal directions, transverse to the axes, so thateach layer forms a plurality of tabs extending generally radially fromthe axes. The horizontal extent of the layers may be controlled byselective deposition during the depositing step, or by selectiveremoval, such as etching, after the depositing step.

The body desirably has two major surfaces as aforesaid, facing inopposite directions. The indentations on the two major surfacesdesirably include pairs of coaxially aligned indentations which mergewith one another to form continuous through holes or via holes extendingthrough the entire body. The steps of providing the body may include thesteps of providing a sheet having holes therein, as by etching the sheetfrom opposite sides to form holes tapering to narrowest points remotefrom the faces of the sheet, and then depositing a coating of adielectric material on the sheet, and in the holes of the sheet, as byelectrophoretic deposition. As further described below, the preferredmethods according to this aspect of the invention provide unique curvedtabs.

These and other objects have features and advantages of the presentinvention will be more readily apparent from the detailed description ofthe preferred embodiments set forth below, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, diagrammatic sectional view depicting portionsof an interposer during one step of a fabrication process according toone embodiment of the invention.

FIGS. 2, 3 and 4 are views similar to FIG. 1 but depicting theinterposer during later stages of the same process.

FIG. 5 is a diagrammatic perspective view depicting a through conductorand contacts of the interposer of FIGS. 1-4.

FIG. 6 is a further view similar to FIGS. 1-4 but depicting thecompleted interposer.

FIG. 7 is a diagrammatic elevational view depicting stacked componentsof the beginning of an assembly process using the interposer of FIGS.1-6.

FIG. 8 is a fragmentary, diagrammatic sectional view depicting a portionof the components illustrated in FIG. 7 at the beginning of the assemblyprocess.

FIG. 9 is a view similar to FIG. 8 but depicting the components at alater stage in the assembly process.

FIG. 10 is a fragmentary, diagrammatic sectional view depicting portionsof an interposer during one step of a fabrication process according toanother embodiment of the invention.

FIGS. 11 through 14 inclusive are views similar to FIG. 10 but depictingthe interposer at progressively later stages of the fabrication process.

FIG. 15 is a diagrammatic, fragmentary plan view of the surface of theinterposer shown in the sectional view in FIG. 14.

FIG. 16 is a view similar to FIGS. 10-15 but depicting the completedinterposer.

FIG. 17 is a diagrammatic perspective view depicting a through conductorand contacts of the interposer of FIGS. 10-16.

FIG. 18 is a fragmentary diagrammatic plan view depicting portions ofstacked components during an assembly process using the interposer ofFIGS. 10-17.

FIG. 19 is a diagrammatic sectional view taken along lines 19—19 in FIG.18.

FIG. 20 is a fragmentary, diagrammatic sectional view on an enlargedscale depicting the components during a later stage of the assemblyprocess.

FIG. 21 is a fragmentary, diagrammatic sectional view depicting aninterposer according to a further embodiment of the invention.

FIG. 22 is a fragmentary, diagrammatic sectional view depicting aninterposer in accordance with yet another embodiment of the invention,in conjunction with other components during one stage of an assemblyprocess.

FIG. 23 is a view taken along line 23—23 in FIG. 22.

FIG. 24 is a view similar to FIG. 22 but depicting a later stage in theassembly process.

FIG. 25 is a view taken along line 25-25 in FIG. 24.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A process in accordance with one embodiment of the invention begins witha body 30 in the form of a sheet of a dielectric material having a firstor top surface 32 and a second or bottom surface 34. The dielectricmaterial should be a material having a relatively high elastic modulussuch as a polyimide material. One suitable polyimide is available underthe trademark UPILEX from the Ube Corporation. Sheet 30 desirably isabout 15-50 microns (“μ”) thick, and most preferably about 25μ thick. Alayer 36 of a temporary layer material susceptible to etching by anetchant which does not attack body 30 is coated on top surface of thebody 30. The temporary layer material desirably is a metal such asaluminum, tin, or nickel which can be removed by etching. Temporarylayer 36 may be about 15-100μ or more thick, most desirably about 50μthick. A second temporary layer 38 similar to layer 36 is applied to thebottom surface 34 of body 30.

Photoresist layers 40 and 42 are applied on the temporary layers 36 and38 and then photographically exposed to develop openings 44 and 46,respectively. Resist layers 40 and 42 may be formed from a conventionalphotoresist material. However, dry film photo resists are preferred. Onesuitable resist is a dry film resist about 25μ thick of the type soldunder the trademark DYNACHEM by Morton Electrical Materials of Tustin,Calif. Openings 44 and 46 are circular, as viewed in directionsperpendicular to surfaces 32 and 34. Also, openings 44 and 46 arecoaxial with one another on a common axis 48 perpendicular to thesurfaces of body 30. Although only a single set of aligned openings isillustrated in the fragmentary view of FIG. 1, aligned numerous sets areprovided in one or more arrays extending over the surfaces of the body.The spacing or “pitch” dimension between adjacent pairs of openings isselected to match the pitch of the pads on the panel or other elementwhich will be mated with the interposer. Preferred structures accordingto this embodiment of the invention can be fabricated with pitchdimensions of 1.5 mm or less, preferably about 0.5 to 1.5 mm.Preferably, each set of aligned openings 44 and 46 are coaxial with oneanother within a tolerance of about 10μ. This degree of alignment can beachieved by conventional film handling and exposure devices such as aconventional two-sided exposure tool. Sheet 30 typically is providedwith sprocket holes (not shown) in margins remote from the area used toform the interposer for handling and aligning the sheet. Alignment basedon such holes normally will be adequate for this step.

In the next stage of the process, the sheet with the temporary layersand photoresist layers is exposed to an etchant, such as a causticsolution, adapted to etch the temporary layers 36 and 38 isotropically.That is, the etchant will attack the temporary layers at substantiallyequal rates in all directions, wherever the temporary layers are exposedto the openings. The etchants attack the first or top temporary layer 36through opening 44 progressively, until the first or top surface 32 ofbody 30 is exposed. At the same time, however, the etchant undercutsphotoresist layer 40, starting from the edge 50 defined by the peripheryof opening 44 and the exposed surface of layer 36. Thus, the etchingprocess forms an aperture 52 in first temporary layer 36, such aperturehaving a wall 54 substantially in the form of a surface of revolutionabout central axis 48. The generator of surface 54 is substantially inthe form of an arc having its center approximately at the top surface oflayer 36, i.e., at the surface of temporary layer 36 remote from body30. Thus, wall 54 is generally in the form of a cup or a section of atoroid. The wall flares radially outwardly, away from central axis 48 inthe vertically outward or upward direction away from body 30, i.e.,upwardly as seen in FIG. 2. Thus, the first or top temporary layer 36includes a rim 55 surrounding each hole 52. Rim 55 has progressivelyincreasing thickness in the radial direction away from common centralaxis 48.

The same etching step also forms apertures 56 in the second or bottomtemporary layer 38, these apertures being similar in configuration anddiameter to apertures 52. Thus, the wall 58 of each aperture 56 isgenerally in the form of a surface of revolution about central axis 48,and flares radially outwardly, away from the central axis, in thevertically upward direction, away from body 30. As used in thisdisclosure with reference to features associated with a surface of abody, the term “upward” means the direction out of such surface, awayfrom the center of the body. Thus, with reference to the second surface34 of body 30, the “upward” direction is the direction toward the bottomof the drawing as seen in FIG. 2. Second temporary layer 38 includesrims of progressively increasing thickness 59 surrounding apertures 56.Each aperture 56 in the second layer 38 is substantially coaxial withthe corresponding aperture in top or first aperture layer 36. Afterconventional rinsing and deactivating steps, holes 60 are formed in body30 by ablating the material of the body. The ablation is performed bydirecting radiant energy onto first surface 32 through the holes 52 inthe top or first temporary layer. The radiant energy may be appliedusing a laser, such as a KrF excimer laser of wavelength 308 nm.Temporary layer 36, and particularly rims 55 immediately surrounding theapertures protect body 30 from the impinging radiant energy. Thus, holes60 are formed in the body of 30. Each hole 60 is coaxial with thecorresponding aperture 52 in a layer 36 an hence with common axis 48 andwith the corresponding aperture 56 in layer 38. The masking action ofthe top layer inherently adjusts the diameter of hole 60 to the diameterof the aperture at the apex of rim 55, i.e., the diameter at thejuncture of rim 55 with sheet top surface 32. Thus, for each set ofapertures, the peripheral wall 54 of the aperture in the top layer, theperipheral wall 62 of the hole 60 and the peripheral wall 58 of theapertures in second or bottom layer 38 are substantially continuous withone another. Absolute smoothness or continuity is not required. Thus,the radiant energy may spread outwardly beneath rim 55 of the firsttemporary layer, causing the diameter of hole 60 to vary slightly fromthe top surface 32 of body 2 to the bottom of surface 34. This may yielda small ridge, less than a few microns high, at the juncture of holesurface 62 with aperture surface 58, at the apex of rim 59. Such ridgesnormally do not impede the process.

After formation of holes 60, additional photoresist layers 64 and 66 areapplied on the first or top temporary layer 36 and the second or bottomtemporary layer 38 respectively. These layers initially bridge over theapertures in the temporary layers and thus hole 60 as well. Resistlayers 64 and 66 may be formed by a dry film resist and may extend overthe apertures and holes in the underlying layers without filling thesame. The photoresist layers are exposed using conventional techniquesto form pairs of openings 68 and 70 in the top and bottom resist layersrespectively in alignment with holes 60 and hence coaxial with theapertures 52 and 56 in the temporary layers 36 and 38. Holes 68 arecircular and slightly larger than the maximum diameter of thecorresponding diameter of the corresponding apertures in layer 36, sothat a small ledge 72 is formed around the periphery of each aperture.Likewise, each hole 70 is slightly larger than the maximum diameter ofthe corresponding aperture 56.

An electrically conductive structural material such as a metal is thendeposited within hole 60 and within the apertures 52 and 56 in thetemporary layer. The deposition process can be performed by seeding thesurfaces of the holes and apertures, as with a palladium salt or otherdeposition promoting agent, and then applying the metal structuralmaterial by plating over the seeded layer. The seeding is performedbefore application of photoresist layers 64 and 66. The structuralmaterial may be applied as a continuous, integral layer 74 covering theperipheral surfaces 62 of the holes in the body and also covering theperipheral walls 54 and 58 of the apertures in the temporary layers. Thestructural material layer should extend radially outwardly from theapertures and covering ledges 72.

The structural material should be relatively ductile. Metals selectedfrom the group consisting of gold, copper, tin, nickel and alloys andcombinations thereof are preferred. Gold is particularly preferred wherethe structural material layer includes only one metal. The structuralmaterial layer desirably is about 2 to about 20μ thick, most preferablybetween about 5μ and about 10μ thick. Alternatively, structural materiallayer 74 may include several sublayers such as a structural metalsublayer, a diffusion barrier sublayer and a corrosion resistingsublayer. Particularly useful sublayered structural metal combinationsare as follows.

TABLE 1 STRUCTURAL DIFFUSION CORROSION METAL BARRIER RESIST CopperNickel Gold Nickel Cobalt Palladium Silver None Pd/Ni Alloy

A further layer 76 of an electrically conductive bonding material isapplied over structural metal layer 74 by conventional depositionprocesses such as electroplating. The electrically conductive bondingmaterial may be a solder, braze, diffusion bonding material, eutecticbonding material, or polymer filled with electrically conductiveparticles. Preferably, the bonding material is adapted to become activeand to bond at a predetermined elevated temperature. Some suitablebonding material compositions are indicated in Table 2 below. In Table2, the entry under the heading “pad surface” refers to the preferred padsurface for mating with the particular bonding material. Also,conventional protective layers, such as a thin gold layer, may beapplied over the conductive bonding material layer 76 to protect thesame from corrosion prior to use.

TABLE 2 TYPE CONDUCTIVE BONDING MATERIAL PAD SURFACE Solder Tin 95%,Silver 5% Tin Solder Tin 60%, Lead 40% Tin Solder Tin 63%, Lead 35%,Silver 2% Gold Braze Tin 94%, Gold 6% Gold Diffusion Gold 80%, Germanium20% Gold Diffusion Gold 80%, Tin 20% Gold Diffusion Tin 90%, Silver 10%Gold Polymer Silver 50% in Epoxy Gold

Structural metal 74 and bonding material 76 thus form integral vias,each such integral via including a through conductor 78 extendingthrough layer 30, a contact 80 on the first side of body 30 and afurther contact 82 on the opposite side of the body. One such via 79 isdepicted in FIG. 5. The first or top-surface contact 80 is generallycup-shaped, and extends radially outwardly, in horizontal directionsaway from central axis 48. The contact thus extends from the first end86 of conductor 78 to a periphery 84 remote from the conductor andremote from central axis 48. The generally cup-shaped contact 80 definesan opening 88 facing upwardly, vertically outwardly, away from conductor78 and hence away from the dielectric body 30 (FIG. 4). In thisembodiment, the entire contact is a body of revolution around thecentral axis 48. Contact 82 at the second or bottom end 90 of conductor78 has a similar configuration, but opens downwardly, in the oppositevertically outward or upward direction away from the second surface 34of the body.

After the vias are formed, they are optionally filled with a flowableconductive fill material 92, as by stenciling or squeegee applicationover the temporary layers and vias. Fill material 92 desirably isarranged to remain solid at temperatures below the activationtemperature of the conductive bonding material 76. Suitable fillmaterials include polymers and polymer precursors with conductiveparticles dispersed therein. The polymeric material may be athermosetting material such as a B-staged or partially cured epoxy or athermoplastic such as a polyimide siloxane. After filling, temporarylayer 36 and 38 are removed by etching with a caustic solution. Theetching process also removes any surface debris left from prior steps.Removal of the temporary layers leaves portions of the contacts spacedvertically from the surfaces of the body. Thus, cup-shaped contact 80 isspaced vertically above first surface 32 of body 30. The spacingincreases progressively from zero at the juncture of the contact withconductor 78 to a maximum at the periphery 84 of the contact. Similarly,contact 82 is spaced in the opposite vertically outward direction awayfrom second surface 34, the spacing increasing from zero at the junctureof the contact with conductor 78 to a maximum at the periphery of thecontact.

After removal of the temporary layers, layers 94 and 96 of a flowabledielectric adhesive are applied on the surfaces of the body. Theflowable dielectric material or adhesive is also selected to flow andform a bond with adjacent dielectric materials at a pre-selectedactivation temperature which is approximately equal to the activationtemperature of conductive bonding material 76. The adhesive may beapplied by methods such as screen printing, application of a dry filmperform and squeegee application. Desirably, the thickness of theadhesive layers is less than the vertical extent of the contacts 80 and82, so that the contacts protrude vertically beyond the adhesive layers.The adhesive may be a material commonly referred to as a “snap-cureadhesive”. In this condition, the interposer is now ready for use.

In a joining process according to a further embodiment of the invention,a plurality of interposers 95, such as the interposers made in theprocess of FIGS. 1-6, are stacked in interleaved, alternatingarrangements with a plurality of circuit panels 98 (FIG. 7) so that oneinterposer is disposed between each pair of adjacent circuit panels andso that the circuit panels and interposers are superposed on oneanother. The circuit panels are generally lamellar structures, i.e.,platelike or sheet-like structures, having major surfaces with contactpads 100 thereon. Panels 98 also have conductors 102 (FIG. 8) extendingin the horizontal directions (the directions to the left and the rightand into and out of the plane of the drawing in FIGS. 7 and 8), as wellas internal through conductors or vias (not shown) interconnecting thepads 100 on oppositely facing major faces of each panel 98 with oneanother. The stacking step serves to align the pads 100 with thecontacts 80 and 82, so that each pad confronts and bears on theassociated contact adjacent to the periphery thereof. Each pad 100 thusbears on the associated contact 80 at locations remote from its centralaxis 48 and at locations where the contact is spaced vertically frombody 30.

In the next stage of the process, the stack is compressed and heated, asby squeezing the stack between heated platens (not shown). Thecompression forcibly engages the contacts of the interposer with thepads of the circuit panels and compresses the contacts 80 and 82vertically and axially in directions parallel to the central axis 48 andtowards the medial plane of the interposer body. As each contact iscompressed axially it expands radially outwardly, in horizontaldirections, away from central axis 48. Thus, the cup-shaped contacts 80and 82 tend to bend downwardly, toward the medial plane of the body, andoutwardly. The action is generally similar to heading or clinching of arivet. As each contact expands outwardly, it wipes across the surface ofthe associated pad 100 on the mating panel. This wiping action isparticularly effective because it occurs under substantial axial orvertical loading during the compressing step.

This action continues as the panels move closer to one another duringthe compressing step, until the assemblage reaches the conditionillustrated in FIG. 9. During this process, the flowable dielectricmaterial or adhesive in layers 94 and 96 fills the spaces between thebody 30 of each interposer and the major surfaces of the adjacentcircuit panels. The dielectric material flows to fill the spaces betweenthe conductors 102 on the surfaces of the panels. This forms asubstantially unitary, multi-layered structure substantially free ofvoids. At the same time, the electrically conductive bonding material 76on the contacts of the interposers forms a metallurgical bond with thepads 100 of the circuit panels. The metallurgical bonding action isgreatly enhanced by the wiping action which occurs during thecompressing step. The fill material 92 within each contact or viastructure flows into engagement with the pads 100 engaged with such viastructure. The flow of this fill material is effectively constrained bythe surrounding walls of the contacts. Accordingly, the fill materialwill not contaminate adjacent features and cause shorting.

An interposer fabrication process according to a further embodiment ofthe invention begins with a conductive, preferably metallic sheet 200(FIG. 10), such as 25% hard rolled and annealed copper about 30-70μthick, typically about 50μ thick. The metal sheet is cleaned usingconventional methods such as sulfuric peroxide etch, rinsed and thenpassivated or protected by washing in a passivating agent such asethylene diazol. Resist layers 202 and 204 are applied on the surfacesof the sheet, as by laminating the layers as dry films. The resistlayers desirably are about 50 microns thick. The resist is cured, as bybaking, and then developed in a pattern including matched pairs ofcylindrical holes 206 and 208 in the top and bottom layers 202 and 204respectively. The holes of each pair are co-axial, on a common centralaxis, 210. The axes 210 are distributed in a regular grid pattern, atspacings as described above, typically 0.5 to 1.5 mm. In the next step,the sheet 200, is etched from both sides using an isotropic etchingsolution. Where the sheet is formed from copper or a copper alloy, theetching solution may be a solution of CuCl and HCl. As the etch attackssheet 200 through the holes in the resist layers it perforates the sheetto form holes 212 centered on axes 210. Each hole 212 has a narrowestpoint or throat 214 adjacent the medial plane 215 of sheet 200, i.e, theplane equidistant from the top and bottom surfaces of the sheet. Eachhole 212 has walls sloping radially outwardly from throat 214 to thesurfaces of the sheet. A relatively slow etch rate, using moderate HClconcentration, is preferred for forming the sloping wall configuration.Each hole 212 may have a minimum diameter of about 100 to about 250microns, preferably about 125 microns. The maximum diameters of eachhole, at the surfaces of the sheet, typically are about 125 to about 300microns.

After the holes are formed, resist layers 202 and 204 are removed. Dots216 of a further resist are applied the top surface of sheet 200. Eachsuch dot may be about 50 microns to about 100 microns in diameter.Resist 216 may have the same composition as resist layers 202 and 204,and may be applied by a similar process. Dots 216 are applied in aregular grid pattern offset from the grid pattern of holes 212 and axes210. As further discussed below, the places covered by dots 216 willultimately form contacts connected to sheet 200, which is used as aplane conductor, such as a ground plane or power plane in the finishedstructure. Accordingly, dots 216 are positioned in a grid matching theground or power plane connection pads on the elements with which theinterposer will be employed.

After application of resist dots 216, a conformal coating of adielectric material 218 is applied over sheet 200. The conformal coatingcovers the sheet 200, including the surfaces within holes 212. Thecoating has a substantially uniform thickness on the surfaces of thesheet and within the holes. Desirably, the coating is between about 20μand about 50μ thick, preferably about 38μ. The dielectric materialpreferably is applied by electrophoretic deposition. In theelectrophoretic deposition process, sheet 200 is electrically connectedto a potential source 220 and immersed with a counter-electrode in abath of liquid electrophoretic deposition mixture. The potential appliedby source 220 deposits solid material from the electrophoreticdeposition mixture. Preferred electrophoretic deposition mixturesinclude materials supplied under the designation Powercron cationicacrylic (700-900 series), or Powercron cationic epoxy (400-600) by thePPG Company. Preferably, the conductive sheet 200 and thecounterelectrode (not shown) extend horizontally in the bath, and aredisposed at a uniform spacing from one another, typically about 2 cm.The counterelectrode should be larger than the sheet, so that thecounterelectrode extends beyond the edges of the sheet. The currentdensity during the electrophoretic deposition step preferably ismaintained below about 1 millipore per square centimeter so as tominimize bubble formation in the deposited coating. Desirably, thecurrent is maintained constant during the deposition process. Thepotential applied may be about 100V, and the process typically takesabout 4 minutes. After the electrophoretic deposition process, thecoated sheet or body is removed from the bath, washed to remove clingingundeposited solution and then baked to cure the deposited coating.

The deposited dielectric body 218 has a first or top surface 222 and asecond or bottom surface 224, and has holes 226 extending entirelythrough the body from the first surface to the second surface. Holes 226extend through the holes 212 of sheet 200 and have walls in the form ofsurfaces of revolution about central axis 210. Each hole 226 has athroat or smallest diameter point adjacent the medial plane of body 218,i.e., approximately at the medial plane 215 of sheet 200, andapproximately midway between first surface 222 and second surface 224.The walls of each hole 226 flare radially outwardly from the centralaxis 210 in the axially outward directions, away from the medial plane215 so that the diameter of each hole 226 gradually increases to amaximum at first surface 222 and second surface 224. Stated another way,each surface 222 and 224 includes a principal, planar portion and theholes form indentations 227 in surfaces 222 and 224, the indentationsmerging with one another at medial plane 215. Resist 216 is removedafter deposition of the dielectric material, typically before thedielectric material is cured. Removal of resist 216 leaves additionalindentations 228 extending inwardly from the first surface of 222 to thedielectric body to the metallic sheet 200.

In the next stage of the process, a structural material, such as thestructural materials discussed above is plated on all of the surfaces ofthe dielectric body 218, including the interior surfaces of holes 226and the indentations 228. The deposition process may include the stepsof seeding the surfaces, as by exposure to a liquid seeding process orby sputter deposition. For example, an adhesion-promoting layer ofchromium, typically about 0.1 microns thick may be applied followed by a1 micron layer of copper. The seed layer 230 contacts metallic sheet 200in indentations 228 and hence is electrically connected to the metallicsheet. The remainder of the structural material is then electroplatedover seed layer 230 as by connecting an electroplating potential source231 to metal sheet 200 and immersing the assembly in an electroplatingbath with a counterelectrode (not shown). The structural materialconforms to the shape of the dielectric body. As the structural materialis deposited, it completely fills the throats or narrowest points ofholes 226 so as to form a solid conductor 233 extending through eachhole 226. However, the structural material does not completely fillthose portions of the holes or indentations adjacent surfaces 222 and224 of the body. Instead, the structural material is deposited as alayer on the outwardly curving walls of holes 226 so as to form anoutwardly flaring, horn-shaped shell 232, integral with conductors 233,within each indentation 227 at surfaces 222 and 224. Similarly,indentations 228 are partially filled by the deposited material, whichforms a similar outwardly flaring shell 234 at the opening of each suchindentation on first surface 222. The structural metal also electricallyconnects each of the outwardly flaring shells 234 to the plane conductoror sheet 200. The structural metal additionally forms planar structures236 covering the principal planar portions of surfaces 222 and 224 ofthe dielectric body.

In the next stage of the process, an additional resist 238 is appliedover the structural metal layer. The structural metal also electricallyconnects each of the outwardly flaring shells 234 to sheet 200. Onceagain, an electrical potential may be applied through sheet 200, andhence applied to the structural metal by way of the shells of layers234. For example, this resist may be deposited to a thickness of about25 microns. One suitable resist is sold under the designation EAGLEelectrophoretic resist by the Shipley company of Marlborough, Mass., andcan be deposited to the desired thickness in about 3 minutes at about200 volts. This resist is then cured by application of a cellulosiccoating, drying and baking. Resist 238 is then exposed and developed inthe conventional manner, using photographic exposure on both sides.

The photographic patterning is arranged to provide generally X-shapedopenings 240 (FIG. 15) in resist layers 238. These openings are inregistration with the shells 232 at through conductors 233 and inregistration with the potential plane shells or vias 234. The openings240 at each shell 232 is symmetrical about the central axis 210 of theshell. Each opening 240 includes a central zone 241 adjacent the centralaxis 210 and further includes slots 242 extending radially outwardlyfrom central region 241, away from the central axis 210. The resistlayer thus has projections 244 extending inwardly towards central axis210. These projections start at locations on the flat metallic sheet 236and extend radially inwardly to locations within the shells 232. Thus,the resist tabs 244 extend axially or vertically downwardly towards themedial plane 215 of the interposer body. Similar X-shaped openings 240are provided at shells 234. As best appreciated with reference to FIG.15, the through holes in the dielectric body, and thus the central axes210, are disposed in a regular, rectilinear grid pattern of rows andcolumns. Slots 242 are arranged on diagonals of this grid. Anelectrically conductive bonding material, such as those discussed aboveis then plated onto the structure, within openings 240. The bondingmaterial thus covers portions of shells 232 and 234 and also coversminor portions of the planar structures 236. At this stage of theprocess, all portions of the structural metal are still electricallycontinuous with sheet 200, and hence an electrical potential for platingcan be applied through sheet 200 for electroplating.

Resist 238 is then stripped and the structural metal is etched. Duringthis etching step, the bonding material 246 acts as an etching mask.Thus, the portions of the structural metal which were previously coveredby resist layers 238 are removed. This exposes the planar parts of firstsurface 222 and second surface 224 of the dielectric body 218, andleaves contacts 250 having shapes corresponding to the X-shapes ofwindows 238. Contacts 250 are provided at both ends of each throughconductor 233. As best seen in FIG. 17, each contact 250 includes agenerally cup-shaped central portion 252, substantially in the form of abody of revolution about central axis 210, having a rim or outer edge atradius R_(c) from the central axis. The contact further includes fourtabs 254 projecting radially outwardly from the rim of the cup-shapedcentral portion, each such tab having a tip 256 at radius R_(t) fromaxis 210. For contacts disposed in a rectilinear grids at a pitch orcontact-to-contact spacing along the rows and columns of the gridbetween about 0.5 and 1.0 mm (about 20 to 40 mils), R_(t) typically isbetween about 100μ and about 230μ. Stated another way, the maximumdiameter of each contact, measured across the tips ofoppositely-directed tabs, is less than about 0.5 mm and desirably lessthan about 400 μm. Preferably, R_(c) is about 40 to about 100μ. Thewidth W_(t) of each tab, typically is about 25 to about 50μ andincreases towards the central portion of the contact. The centralportion 252 of each contact 250 is disposed within one of theindentations 227 in the surfaces 222 and 224 of the dielectric body,whereas the tabs 254 project vertically or axially outwardly from thecentral portions, and extend outwardly from the indentations in thesurfaces to the surrounding planar portions of body surfaces. Tabs 254extend along the diagonals to the rectilinear grid of axes 210. The tabsand central portions include a continuous structural metal layer 258,including portions originally formed as shells 232 and other portionsoriginally included in the planar structures 236. The structural metallayer 258 of each contact 250 is continuous with the structural metal ofthe associated through conductor 233. The tabs and the central, cup-likeportions slope radially outwardly, away from axis 210 in the verticallyor axially outward direction, away from the medial plane of the body. Inthe same manner, the shells 232 are converted into plane-conductorcontacts 252 (FIG. 16). Each such plane-conductor contact hassubstantially the same configuration as the through conductor contacts250, but is metallurgically bonded to the plane conductor or sheet 200.

The interposer of FIGS. 10-17 may be assembled with circuit panels orother microelectronic components in an assembly procedure similar tothat described above. In the assembly process, one of the interposers isstacked between each pair of circuit panels 260. Circuit panels 260 haveinternal plane conductors 261. Panels 260 also have signal pads 262disposed in a regular, rectilinear grid pattern corresponding to therectilinear grid of through conductors 233, contact axes 210 andcontacts 250 in the interposer, and also have plane conductor connectionpads 264, such as ground or power plane connection pads, at certainlocations between signal pads 262. Pads 262 and 264 are substantiallysquare. The sides of the pads extend in the row and column direction ofthe array of pads and hence the diagonals are aligned with the diagonalsof the array.

In the stacking procedure, the signal pads 262 are brought intoregistration with the signal contacts 250, whereas the potential planepads 264 are registered with plane conductor contacts 252. When the padsare brought into registration with the contacts 250, the tabs 254 of thecontacts are aligned with the diagonals of the square pads 262. Acontact 250 is illustrated in the broken lines in FIG. 18 superposed onone pad 262. All of the other signal contacts 250 and plane conductorcontacts 252 are similarly oriented on the associated pads. Althoughonly two panels and one interposer are illustrated in FIG. 19, thestacking step may be performed with any number of panels and interposersinterleaved with one another.

In this process as well, the stacked elements are compressed and heated.Desirably, a vacuum is applied during the compressing step to remove airfrom between the panels and interposers. As the stacked elements arecompressed, the pads 262 of the circuit panels bear on the peripheriesof the contacts 250, i.e., on the tabs 254 adjacent to tips thereof. Asbest illustrated in FIG. 20, this action tends to bend the tabsdownwardly towards the medial plane 215 of the interposer, and tends toforce each tab 254 into the adjacent surface 222 or 224 of thedielectric body 218. The heat applied during this procedure softensdielectric 218 and hence facilitates bending of the tabs. As the tabbends downwardly, the tip of the tab moves radially outwardly form thecentral axis 210 of the contact. This again causes the surface of thetab to wipe over the surface of the engaged pad. As pointed out above,the wiping action promotes formation of an effective electricalconnection. Because the tabs are separated from one other at their tips,the tabs can be bent radially outwardly in this fashion without tearingor substantially cracking the structural material. Further, theindividual tab tips have relatively small surface areas, and can bepushed into the underlying dielectric 218. The cup-shaped centralportion 251 of each contact tends to be more rigid than the tabs.However, the central portion is disposed in an indentation in the bodysurface, so that the central portion recessed relative to the tips ofthe tabs and relative to the principal plane of the body surface. Thecentral portion therefore does not engage the pad and does notsubstantially impede bending of the tabs. The plane conductor contacts252 operate in the same manner. The heat applied during the process alsoactivates the conductive bonding material 246 so as to form a permanentconnection between the tabs of the contact and the associated pad.

The dielectric material on the interposer desirably flows to an extentsufficient to fill spaces between the interposers and panels, includingspaces around the raised conductors on the panel surfaces. Thedielectric material of the interposer preferably also adheres to thematerials of the circuit panel. To promote adhesion, the dielectricmaterial may be only partially cured during the interposer fabricationstep. Curing of the dielectric material may be completed during thecompression and heating steps of the assembly process.

Numerous variations and combinations of the features described above canbe utilized without departing from the present invention as defined bythe claims. In one such variant, the surfaces of the contacts whichengage the pads may be provided with small bumps or asperities toprovide a scraping action during the wiping motion. Alternatively oradditionally, asperities can be provided on the contact pads of thecircuit panels. The asperities can be formed from the structuralmaterial, or preferably, from the electrically conductive bondingmaterial on the surfaces of these elements.

Although the interposers typically are used in engagement with circuitpanels to form multi-layer circuitry, they can also be employed withother microelectronic elements, such as semiconductor chips, active orpassive components, flat flexible cables and the like. The componentsincorporating the contacts are referred to herein as “interposers”because the components commonly used between other elements, but theinterposers need not be configured for such use. For example, aninterposer may have only one surface bearing contacts, and the contactsmay be linked to a plane conductor, to through conductors, or otherconductors on or within the interposer. The interposer body can beintegral with the body of a microelectronic component such as asemiconductor chip, a printed circuit board, a ceramic or othermulti-chip module base, a flex cable, a chip capacitor or othermicroelectronic components. For example, as illustrated in FIG. 21, aninterposer body 300 includes a dielectric layer 302 deposited on thefront surface 304 of a semiconductor chip 306. Dielectric sheet 302 isprovided with holes 306 in alignment with the connection pads 308 of thechip. Contacts 310, similar to contacts 250 discussed above withreference to FIGS. 10-20, are provided at holes 306. Each contact 310 ispermanently connected to the associated connection pad 308 of the chip,and hence connected to the internal electrical conductor 312 of thechip. For example, the contact may be metallurgically bonded to theconnection pad of the chip during a deposition process used to form thecontact. The exposed surface 314 of dielectric layer 302 constitutes thefirst or contact-bearing surface of this single-sided interposer. Inuse, this first surface is juxtaposed with a surface of a substrate orother electrical component, and the contacts are engaged with connectionpads on the substrate and bonded thereto using a process substantiallyas discussed above. The contacts in this structure as well mayincorporate electrically conductive bonding material, and the dielectriclayer 302 may incorporate flowable dielectric materials, adhesives orthe like.

In other variants of the invention, contacts having outwardly projectingtabs may include more than four or fewer than four tabs. Also, the tipsof the tabs are positioned above the surface of the interposer body,with a gap therebetween to facilitate downward bending of the tabs.

The structures illustrated in FIGS. 22-25 have contacts 425incorporating such gaps. Each contact 425 includes a central portion451. Each such central portion is generally in the form of a hollow bodyof revolution having a central axis 410 perpendicular to the surface 422of the interposer and a generator curving away from the central axis.The central portions of the contacts merge with tubular throughconductors 480 adjacent the medial plane 415 of the interposer body. Asmall rim 429 extends radially outwardly, away from axis 410, at the topend of the central portion, remote from the medial plane.

Four tabs 454 are connected to the rim of each contact. The tabs extendradially outwardly, away from the central axis. Each tab has a smallbump or asperity 461 adjacent its radially outermost tip 456. As bestseen in FIG. 23, the tips of tabs 454 are rounded as seen in plan view.The edges of each tab slope away from one another in the radially inwarddirection, away from the tip 456 of the tab, so that each tab widens andjoins smoothly with rim 429 of the central portion and with the nextadjacent tab. Thus, the tabs cooperatively define a structure in theform of a rounded and smooth X-shape, with curved edges at juncturesbetween adjacent tabs, i.e., at the junctures of the tabs and rim 429.The peripheral portions of each contact, including at least the tips oftabs 454 are spaced vertically above the surfaces of the interposerbody, so that there are gaps 455 below the tips of the tabs.

The interposer body includes a metallic sheet or plane conductor 400similar to the plane conductors discussed above, together with acomposite dielectric layer. The composite includes a first layer 418 ofan electrophoretically deposited polymer, desirably a thermosettingpolymer such as the epoxy compositions discussed above, in contact withthe plane conductor or sheet 400. A second layer of a flowabledielectric material, such as a relatively heat-resistant thermoplasticmaterial, overlies the first layer. One such flowable dielectricmaterial which may be used is a polyetherimide sold under the registeredtrademark ULTEM.

Structures according to this arrangement can be fabricated usingtechniques similar to those discussed above. Thus, the interposer bodycan be formed using deposition techniques similar to those used to formthe interposer body of FIGS. 10-20. A temporary layer similar to thosediscussed above with reference to FIGS. 1-9 is then applied on thesurfaces of the body and removed after deposition of the structuralmaterial of the contacts and through conductors. As in the processesdiscussed above, removal of the temporary layer leaves the peripheralportions of the contact, in this case including tabs 454, spacedvertically above the surfaces of the interposer body.

In an assembly process, the interposer is stacked with circuit panelsother microelectronic devices, and then compressed. One such panel orelement 460 is juxtaposed with each surface of the interposer. Thecondition of the assembly immediately after stacking but beforecompression is shown in FIGS. 22 and 23. As discussed above, the panelshave square connection pads 462, and tabs 454 lie along the diagonals ofthe square connection pads. When the stacked elements are compressed,the contacts deform as indicated schematically in FIGS. 24 and 25. Thetabs 454 deform radially outwardly, away from the central axis 410, andalso bend downwardly, into engagement with the adjacent surfaces 422 ofthe body. In this action, the tips 454 of the interposer and asperities461 on the tabs wipe radially outwardly over the surfaces of connectionpads 462. The joining material on the contacts thus can form aneffective bond between the tabs and the connection pads. The downward oraxial movement of the contact periphery, particularly of tabs 454 alsocompensates for vertical tolerances in the assembly. That is, if theconnection pads 462 of the mating elements are not perfectly coplanar,or if the contacts themselves vary slightly in height, the differenceswill be taken up by differences in the amount of deformation in thetabs. This contributes to the reliability of the assembly.

The dielectric materials of the interposer, particularly the flowabledielectric adhesive 419, fill any minor spaces beneath the contacts andaround the contacts and the connection pads. Here again, the dielectricmaterials also fill spaces around irregularities on the surfaces of thecircuit panels. For example, where the circuit panels have conductors ontheir exposed surfaces, the dielectric materials desirably fill thespaces between such conductors so as to provide a substantiallyvoid-free interface.

In still further variants, the fill material used in the embodiment ofFIGS. 1-9 may be omitted or, conversely, such a fill material can beincluded in the structure of FIGS. 10-20, as by positioning the fillmaterial within the cup-shaped central portions 251 of the contacts.Also, the dielectric interposer body can be fabricated by othertechniques. For example, the dielectric material of the body can bemolded, as by injection molding, compression molding, plastisoltechniques, solvent casting or other known molding techniques. Themolded part may have holes and indentations shaped as discussed abovewith reference to FIGS. 10-20. A plane conductor may be incorporated insuch a molded part, as by insert molding. As these and other variationsand combinations of the features discussed above can be utilized withoutdeparting from the present invention, the foregoing description of thepreferred embodiments should be taken by way of illustration, ratherthan by of limitation of the invention described in the claims.

What is claimed is:
 1. An interposer for making connections toelectrical pads on a surface of a microelectronic element, theinterposer comprising: (a) a body having a first major surface, and asecond major surface facing in the opposite direction from said firstmajor surface, said body having horizontal directions parallel to saidsurfaces, and vertical directions perpendicular to said surfaces; (b) aplurality of conductors extending through said body between saidsurfaces, said conductors having first ends and second ends; (c) aplurality of first contacts at said first major surface, each firstcontact being permanently joined to one of said first ends and extendingradially outwardly in at least two of said horizontal directions overthe first surface of the body away from the conductor, each firstcontact having a periphery remote from the conductor, each first contactbeing adapted to deform so that the periphery of each first contact willexpand radially outwardly away from the joint of each first contact andthe conductor responsive to a vertical force toward said body applied toeach first contact, whereby each first contact will wipe the pads of amicroelectronic element when the microelectronic element is juxtaposedwith said first surface and forced toward said body; and d) a pluralityof second contacts at said second major surface, each second contactbeing permanently joined to one of said second ends and extendingradially outwardly in at least two of said horizontal directions overthe second surface of the body away from the conductor, each secondcontact having periphery remote from the conductor, each second contactbeing adapted to deform so that the periphery of each second contactwill expand radially outwardly away from the joint of each secondcontact and the conductor responsive to a vertical force toward saidbody applied to each second contact, whereby each second contact willwipe the pads of a microelectronic element when the microelectronicelement is juxtaposed with said second surface and forced toward saidbody.
 2. The interposer of claim 1, wherein said body having saidhorizontal directions parallel to said first major surface defining ahorizontal plane, and each said contact at said first major surfacehaving a peripheral portion extending radially outwardly proximate tosaid horizontal plane defined by said first major surface.
 3. Aninterposer as claimed in claim 1 wherein said second end contacts definerecesses opening vertically upwardly, the interposer further comprisinga flowable conductive material disposed in said recesses.
 4. Theinterposer of claim 1, wherein said body having said horizontaldirections parallel to said first major surface defining a horizontalplane, and each said second end contact having a peripheral portionextending radially outwardly proximate to said horizontal plane definedby said first major surface.
 5. An interposer as claimed in claim 1wherein said first contacts define recesses opening vertically upwardly,the interposer further comprising a flowable conductive materialdisposed in said recesses.
 6. An interposer as claimed in claim 1wherein said flowable conductive material includes a polymer selectedfrom the group consisting of partially cured and uncured epoxies andthermoplastics, and further includes a particulate filler selected fromthe group consisting of silver, gold, gold plated nickel, and goldplated glass.
 7. An interposer as claimed in claim 1 wherein each saidcontact at said first major surface is adapted to deform so that theperiphery of the contact moves vertically downwardly, towards the body,as well as radially outwardly away from the associated conductor.
 8. Aninterposer as claimed in claim 7 wherein the periphery of each saidcontact at said first major surface is spaced vertically above saidbody, with a gap between the periphery of said contact and said body. 9.An interposer as claimed in claim 8 wherein each said contact at firstmajor surface has a central portion attached to an associated conductorand peripheral portion extending radially outwardly from the centralportion.
 10. An interposer as claimed in claim 9 wherein each saidcentral portion is generally in the form of a body of revolution about avertical axis normal to said first surface, each said central portionhaving a rim remote from the associated conductor, the peripheralportion of each said contact at said first major surface being connectedto the rim of the central portion.
 11. An interposer as claimed in claim10 wherein said body of revolution includes a portion of a substantiallytoroidal surface.
 12. An interposer as claimed in claim 9 wherein eachsaid central portion is in engagement with said body and each saidperipheral potion extends upwardly away from said body.
 13. Aninterposer as claimed in claim 9 wherein each said peripheral portionincludes a plurality of tabs extending from an associated centralportion.
 14. An interposer as claimed in claim 13 wherein said bodyincludes a plurality of indentations in said first surface, and saidcentral portions of said first contacts include rims remote from saidconductors, said rims of said central portions being disposed in saidindentations and recessed from said first surface of said body, each oneof said plurality of tabs extending out of an associated indentation.15. An interposer as claimed in claim 1 wherein each said contact atsaid first major surface includes a plurality of tabs extending radiallyoutwardly away from the associated conductor, each said tab having a tipremote from the conductor.
 16. An interposer as claimed in claim 15wherein said tabs of each said contact at said first major surface aredisposed in a substantially symmetrical pattern about the juncture ofthe contact and the associated conductor.
 17. An interposer as claimedin claim 16 wherein each said contact at said first major surfaceincludes four said tabs, and said substantially symmetrical pattern is aquatrefoil pattern.
 18. An interposer as claimed in claim 7 wherein saidcontacts at said first major surface are disposed in a substantiallyrectilinear grid having rows and columns, and wherein said tabs extendsubstantially diagonally with respect to said rows and columns.
 19. Aninterposer as claimed in claim 15 wherein said tips of said tabs arevertically spaced from said body.
 20. An interposer as claimed in claim1 wherein each said second end contact includes a plurality of tabsextending radially outwardly away from the associated through conductor,each said tab having a tip remote from the conductor.
 21. An interposeras claimed in claim 20 wherein said tabs of each said second end contactare disposed in a substantially symmetrical pattern about the junctureof the second end contact and the associated through conductor.
 22. Aninterposer as claimed in claim 21 wherein each said second end contactincludes four said tabs, and said substantially symmetrical pattern is aquatrefoil pattern.
 23. An interposer as claimed in claim 22 whereinsaid second end contacts are disposed in a substantially rectilineargrid having rows and columns, and wherein said tabs extend substantiallydiagonally with respect to said rows and columns.
 24. An interposer asclaimed in claim 20 wherein said tips of said tabs are vertically spacedfrom said body.
 25. An interposer as claimed in claim 1 wherein eachsaid second end contact is formed integrally with the associated throughconductor.
 26. An interposer as claimed in claim 25 wherein each saidassociated through second end conductor extends substantiallyperpendicular to said first surface.
 27. An interposer as claimed inclaim 1 wherein each said contact at said first major surface is formedintegrally with the associated conductor.
 28. An interposer as claimedin claim 27 wherein each of said plurality of conductors extendsubstantially perpendicular to said first surface.
 29. An interposer asclaimed in claim 1 wherein the each said second end contact is adaptedto deform so that the periphery of the second end contact movesvertically, towards the body, as well as radially outwardly away fromthe associated through conductor.
 30. An interposer as claimed in claim29 wherein the periphery of each said second end contact is spacedvertically away from said body, with a gap between the periphery of saidsecond end contact and said body.
 31. An interposer as claimed in claim30 wherein each said second end contact has a central portion attachedto the associated through conductor and a peripheral portion extendingradially outwardly from the central portion.
 32. An interposer asclaimed in claim 31 wherein each said central portion is in engagementwith said body and each said peripheral portion extends away from saidbody.
 33. An interposer as claimed in claim 31 wherein each said centralportion is generally in the form of a body of revolution about avertical axis normal to said first surface, each said central portionhaving a rim remote from the associated through conductor, theperipheral portion of each said second end contact being connected tothe rim of the central portion.
 34. An interposer as claimed in claim 31wherein each said peripheral portion includes a plurality of tabsextending from the associated central portion.
 35. An interposer asclaimed in claim 34 wherein said body includes a plurality ofindentations in said second surface, said rims of said central portionsbeing disposed in said indentations and recessed from said secondsurface of said body, each said tab extending out of the associatedindentation.
 36. An interposer as claimed in claim 33 wherein said bodyof revolution includes a portion of a substantially toroidal surface.